Method for treatment of waste metal and liquid dross

Abstract

In a method for treating liquid dross wherein the dross is situated in a skimming trough and charged into a rotating, substantially horizontal cooling pipe through which it passes so that the dross is cooled to a temperature below the melting point thereof to obtain a granulated form, the dross is charged from the skimming tank into the cooling pipe and passed therethrough substantially in the absence of air or oxygen whereupon the cooled granulated dross is subjected to an autogenous grinding process, the ground dross then being separated into a granulated metal fraction and a fine-grained fraction. Apparatus for performing the method of the invention includes a hood located over the inlet side of the cooling pipe so that the entrance of air into the pipe is substantially prevented. The skimming trough is sealingly engaged to the hood so that the dross is charged from the skimming trough into the cooling pipe without any substantial contact with the air. An autogenous grinding mill is provided having an inlet communicating with an outlet opening of the cooling pipe.

What is claimed is: 
     
       1. In a method for treating liquid dross obtained from metal smelting and remelting operations, such as in connection with aluminum extraction, including the steps of pouring the dross from the melting furnace into a skimming trough, charging the dross from the skimming trough into a rotating, substantially horizontal cooling pipe, passing the dross through the cooling pipe from one end to the other so that the inner surface thereof is at least partially wetted thereby, and so that the dross is cooled to a temperature below the melting point thereof and wherein it is granulated, the improvement comprising: conducting the steps of charging the dross from the skimming trough into the cooling pipe and passing the dross through the cooling pipe substantially in the absence of air or oxygen;   subjecting the granulated dross to an autogenous grinding process; and   separating the ground dross into a granulated metal fraction and a fine-grained fraction, the latter fraction containing substantially powdered metal oxide.   
     
     
       2. The method of claim 1 wherein said steps of charging and passing the dross are carried out in an inert atmosphere. 
     
     
       3. The method of claim 2 wherein said separating step is carried out by screening the ground dross. 
     
     
       4. The method of claim 1 wherein said step of charging the dross from the skimming trough into the cooling pipe comprises introducing the dross into the pipe by means of a bucket elevator. 
     
     
       5. The method of claim 1 wherein said step of subjecting the granulated dross to an autogenous grinding process includes passing the cooled dross from the cooling pipe into a grinding drum through a discharge opening provided at one end of the cooling pipe, and wherein the dross is directed at the discharge opening to substantially constitute a sealing medium between the cooling pipe and the grinding drum. 
     
     
       6. The method of claim 1 wherein said step of charging the dross from the trough into the cooling pipe comprises intermittently charging dross into the cooling pipe so that the cooling thereof in the pipe is accomplished intermittently. 
     
     
       7. The method of claim 1 wherein said separating step is carried out by screening the ground dross and further including the steps of exhausting fine dust produced during the autogenous grinding step during the screening of the dross.